Electroacoustic transducers

ABSTRACT

A rugged low-cost transducer is used in a multiple array to provide greater power with a more precise sound pattern. The transducers are cylindrical elements which are partially recessed in a rigid baffle plate or housing structure. The only radiation takes place from the exposed parts of the cylindrical transducer shell.

United States Patent [191 Barrow [11] 3,736,555 1 May 29, 1973 [54] ELECTROACOUSTIC TRANSDUCERS [75] Inventor: Gilbert C. Barrow, Scituate, Mass.

[73] Assignee: Massa Division, Dynamics Corporation of America, Hingham, Mass.

[22] Filed: Aug. 20,l97l

[2]] Appl. No.: 173,476

[52] US. Cl ..340/8 [51] Int. Cl. ..H04b 13/00 [58] Field of Search ..340/8, 9, 10, 11,

[56] References Cited UNITED STATES PATENTS 2,989,725 6/1961 Miller ..340/9 8/1960 Harris ..340/l0X 12/1962 Roth ..340lll Primary Examiner-Robert F. Stahl Assistant Examiner-Harold Tudor Attorney-Louis Bernat [57] ABSTRACT A rugged low-cost transducer is used in a multiple array to provide greater power with a more precise sound pattern. The transducers are cylindrical elements which are partially recessed in a rigid baffle plate or housing structure. The only radiation takes place from the exposed parts of the cylindrical transducer shell.

9 Claims, 4 Drawing Figures PATENTEU MAY 29 I973 INVENTOR G/LBERT C. BAR/70W 1 ELECTROACOUSTIC TRANSDUCERS My invention relates to electroacoustic transducers, and more particularly to transducers which operate under water, for sonar and similar applications. My invention is particularly useful for transducers operating in either the higher audible frequency region or the ultrasonic frequency region.

Prior art underwater transducers for producing a directional sound radiation pattern have employed an array of inertial mass loaded, vibrating pistons, driven by magnetostrictive or piezoelectric transducer means. One type of these transducers generates vibratory forces between an inertial mass and a sound radiating piston, such as is illustrated in US. Pat. No. 3,328,751.

Another type of prior art directional underwater transducer employs longitudinal resonating electromechanical transducer elements, such as is illustrated in U.S. Pat. No. 2,427,062. The vibrating, sound radiating mass of these prior art piston" type transducers have a relatively large inertia. This inertia, in turn, limited the band width of the frequency-response characteristics. Thus. as transmitters, these transducers are limited because of the inherently high mechanical Q of the vibrating system.

Accordingly, a primary object of my invention is to provide a directional underwater electroacoustic transducer having a relatively low vibrating mass, as compared to prior art structures. A related object is to achieve a relatively broad band of frequency-response, with high efficiency.

Another object of my invention is to provide a directional underwater electroacoustic transducer which utilizes the radiation from an array of cylindrical transducer elements.

Still another object of my invention is to provide a low-cost, high efficiency underwater transducer which has a low mechanical Q, with a resulting broad band response.

Yet another object of my invention is to provide a low-cost, rugged transducer structure capable of with standing underwater explosive shock.

In keeping with an aspect of the invention, these and other objects are accomplished by a rugged, low-cost transducer used in a multiple array, to provide a greater sonic power output. The transducers are cylindrical shell elements which are partially recessed in a rigid baffle plate or housing structure. The only radiation from the transducer takes place from the exposed parts of the cylindrical shell (i.e., not the part recessed in the baffle). As a result of this structure, the inertia of the transducer is reduced, as compared to the piston type, yet a high efficiency is maintained, with a low Q, broad band response.

The invention itself, both as to its organization and method of operation, as well as advantages thereof, will best be understood when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a plan view illustrating one particular embodiment of my invention in which a number of cylindrical transducer elements are arranged to provide a piston-like radiating array, to achieve a directional pattern;

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1;

FIG. 3 is a plan view of another embodiment of my invention, in which a plurality of cylindrical transducer elements are arranged in a linear array of piston-like radiating surfaces; and

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3.

In FIGS. 1 and 2, a rigid plate member 10 might be made from steel, for example, or from any other suitable rigid material. Into the front surface 12 of the plate member -10 are formed two or more parallel, semicylindrical recesses 13. For illustrative purposes, a plurality of cylindrical transducer elements 14 may be polarized ceramic piezoelectric cylinders, having electrode surfaces on both the inside and outside walls of the cylinders, as known in the art. Two or more of these transducer elements are mounted in the recesses 13. For the illustrative construction here shown, a thin layer of low acoustic impedance material 17, such as corprene, is employed as a liner between the surfaces of thexrecessed semi-circular grooves 13 and the outside peripheral surfaces of the ceramic cylinders 14.

Preferably, the cylindrical transducer elements are assembled so that approximately 50 percent of the surface remains above the front face 12 of the rigid plate 10. The other 50 percent is recessed in the grooves 13. If the linear dimensions of the plate member 10 are greater than one wavelength of sound, generated at the operating frequency, the plate 10 acts as a large rigid baffle. A mirror image of the exposed top half of the cylinders is effectively created by the plate 10.

The outside electrode surfaces of the transducer cylinders are connected together by electrical conductors 15 which, for example, may be soldered to the outer electrode surfaces. The inside electrode surfaces may be similarly connected together by the electrical conductors 16, as schematically illustrated in F IG. 1. A waterproof cable 18 has an internal conductor 19 connected to the outer electrode surfaces of the transducers by means of a conductor 20. Another internal cable conductor 21 is connected to the inner electrodes of the transducers by means of a conductor 22.

After the'electrical connections are made and the structural assembly is completed, a sound transparent, waterproof material 23 is sealed to the front surface 12 of the rigid plate member 10. The material 23 protectively encloses the transducer element assembly to enable an operation of the transducer in an underwater environment. The waterproof material 23 may be any suitable compound, which is similar to molded rubber or to a waterproof sound conducting material, such as polyurethane.

An external A.C. source S is connected through the cable 18 to drive the transducers. When so driven, the surface of the transducer elements 14 executes radial vibrations,

The structure illustrated in FIG. 1 results in a composite transducer having an effective piston radiating surface which is equivalent to the projected area of the transducer element array. If the plate member 10 has width and length dimensions exceeding approximately one wavelength of the sound being generated at the highest frequency of operation, the transducer generates a directional beam of sound radiated from the front side of the assembly. The sound radiated from the back of the structure (i.e., from the back of plate 10) is reduced. The beam angle gets progressively smaller as the size of plate 10 increases relative to the wavelength and as the total number of transducer elements increases in the assembled array.

Another type of construction that embodies the same principles is shown in FIGS. 3 and 4. In this case the plate member 10, of FIG. 2, is replaced by an elongated plate 31 having a funnel or channel cross-section which is constructed in the form illustrated in FIG. 4. A number of cylindrical ceramic transducers 32 are assembled as a linear array, with a portion of the outside surface of the cylinders mounted in a semi-circular recess 33 at the root of the funnel or channel. A corprene liner 34 is preferably placed between the outer surfaces of the ceramic cylinders 32 and the mating contoured surface 33 of the plate 31. The inner and outer electrode surfaces of the ceramic cylinders 32 are interconnected by wires 37, 38, and the electrical terminals are then connected to the internal conductors of an underwater cable 35.

To complete the assembly, a sound transparent waterproof material 36 is sealed to the front of the funnel or channel surface of the plate structure 31. This waterproof covering serves the same function as the material 23, shown in FIG. 2.

The transducer cylinders 32 are preferably arranged so that approximately one-half of the outer cylinder is shielded by the corprene liner 34, and the other half of the surface is exposed for radiating sound through the encapsulating material 36. The flared sides of the flange plate 31 are here shown as being set at an angle which is less than 180. This disclosure is selected as illustrative of the case where the horizontal radiation beam angle from the transducer is somewhat sharper than it would be if the flanged portions of the plate 31 were formed at an angle of 180.

For the best operation of the embodiment of FIGS. 3 and 4, it is necessary for both the overall width of the plate member 31 and the length of the plate to exceed one wavelength of sound, at the operating frequency. For this condition, the plate member 31 acts as a large rigid baffle. As compared to the embodiment of FIG. 1, the flare of plate 31 increases the ratio of acoustic energy radiated from the front side of the assembly, rel ative to the radiation which spills over and around to the back of the transducer assembly.

The description of the transducer assembly has been given as using ceramic cylinders for the transducer elements. Alternately the cylinders 14 and 32 could be replaced, for example, by magnetostrictive nickel tubes with a toroidal winding around the periphery of the cylindrical shells. This structure operates as a magnetostrictive vibrator without changing the principle of my invention.

The preferred arrangement is achieved when 50 percent of the vibrating cylindrical surface is embedded in the rigid baffle. However, the inventive transducer is also operative if either more or less than 50 percent of the surface is embedded into the recessed surface of the baffle plate.

Among the advantages of the described structure is that a more economical directional array of transducers can be produced, as compared with the cost of similar conventional transducer arrays, which utilize mass loaded vibrating pistons, for example. Also, the walls of the cylinders form the total vibrating diaphragm, and they are much lighter than a corresponding array of comparable vibrating pistons. The band width of the response-frequency characteristic of the inventive transducer can be made greater than the band width of the conventional transducer. Moreover, any suitable and convenient array configuration of cylindrical elements may be used to achieve any desired beam pattern. Also, to achieve maximum efficiency, the diameter of the cylinders is selected to place resonance near the center point of the frequency range of operation. Finally, the wall thickness of the cylindrical transducer elements is selected to control the transducer band width.

While several specific embodiments have been shown and described, various modifications and alternative constructions may be made without departing from the true spirit and scope of the invention. Therefore, the appended claims are intended to cover all equivalent structures falling within the true spirit and scope of the invention.

I claim:

1. An electroacoustic transducer comprising a rigid plate member having front and rear surfaces with at least one concave groove-like recess having a semicircular cross section formed within said front surface, said recess having an axis of symmetry lying parallel to said front surface, at least one cylindrical tubular transducer element having a longitudinal axis and an external surface with a circular cross section co-axially positioned around said longitudinal axis, said transducer element comprising means for executing radial vibrations of said surface when driven by electrical power from an alternating current source, said cylindrical transducer being mounted in said semi-circular concave recess with a first portion of said tubular surface being surrounded by walls of said recess and another portion of said surface being exposed above said front surface, electric conductor means for connecting said alternating current source to said transducer element, and waterproof sound transparent means sealed to said rigid plate member and waterproofingly covering the exposed surfaces of said transducer elements.

2. The transducer of claim 1 wherein there are a plurality of said concave recesses and a plurality of said transducer elements, each of said transducer elements being mounted within an associated slot, with the axes of the transducer elements parallel to the axes of the slots.

3. The transducer of claim 2 wherein the relative dimensions of said slots and elements are such that approximately 50 percent of the external surface of each tubular element is mounted within a slot and approximately 50 percent of the external surface of each tubular element remains above the front surface of said rigid plate member.

4. The transducer of claim 1 wherein said plate member has length and width dimensions, each of which dimensions exceeds one wavelength of sound at the frequency of operation of the transducer.

5. The transducer of claim 1 and a layer of pressure release material between the outer surface of the tubular transducer element and the surface of the concave groove within which the tubular element is mounted.

6. The transducer of claim 1 further characterized in that said transducer element is a polarized ceramic cylinder.

7. The transducer of claim 5 further characterized in that said transducer element is a polarized ceramic cylinder. I

8. The transducer of claim 1 further characterized in that said transducer element is a magnetostrictive tube.

9. The transducer of claim 5 further characterized in that said transducer element is a magnetostrictive tube. k 

1. An electroacoustic transducer comprising a rigid plate member having front and rear surfaces with at least one concave groovelike recess having a semi-circular cross section formed within said front surface, said recess having an axis of symmetry lyIng parallel to said front surface, at least one cylindrical tubular transducer element having a longitudinal axis and an external surface with a circular cross section co-axially positioned around said longitudinal axis, said transducer element comprising means for executing radial vibrations of said surface when driven by electrical power from an alternating current source, said cylindrical transducer being mounted in said semi-circular concave recess with a first portion of said tubular surface being surrounded by walls of said recess and another portion of said surface being exposed above said front surface, electric conductor means for connecting said alternating current source to said transducer element, and waterproof sound transparent means sealed to said rigid plate member and waterproofingly covering the exposed surfaces of said transducer elements.
 2. The transducer of claim 1 wherein there are a plurality of said concave recesses and a plurality of said transducer elements, each of said transducer elements being mounted within an associated slot, with the axes of the transducer elements parallel to the axes of the slots.
 3. The transducer of claim 2 wherein the relative dimensions of said slots and elements are such that approximately 50 percent of the external surface of each tubular element is mounted within a slot and approximately 50 percent of the external surface of each tubular element remains above the front surface of said rigid plate member.
 4. The transducer of claim 1 wherein said plate member has length and width dimensions, each of which dimensions exceeds one wavelength of sound at the frequency of operation of the transducer.
 5. The transducer of claim 1 and a layer of pressure release material between the outer surface of the tubular transducer element and the surface of the concave groove within which the tubular element is mounted.
 6. The transducer of claim 1 further characterized in that said transducer element is a polarized ceramic cylinder.
 7. The transducer of claim 5 further characterized in that said transducer element is a polarized ceramic cylinder.
 8. The transducer of claim 1 further characterized in that said transducer element is a magnetostrictive tube.
 9. The transducer of claim 5 further characterized in that said transducer element is a magnetostrictive tube. 